1. Field of the invention
This invention relates to a process for the preparation of a stabilizer for synthetic resins such as a chlorine-containing resin, acrylonitrile -- butadiene -- styrene copolymer, methyl methacrylate -- butadiene -- styrene copolymer and the like. In particular, this invention relates to a process for the preparation of a stabilizer for synthesic resins mainly consisting of a molecular weight increased alkyltin mercaptocarboxylic acid ester having little odor and being excellent in lubricating effect which comprises interesterification between a certain alkyltin mercaptocarboxylic acid ester and an alcohol.
2. Description of the prior art
In general, such synthetic resins as chlorine-containing resin, acrylonitrile -- butadiene -- styrene copolymer, methyl methacrylate -- butadiene -- styrene copolymer and the like, especially a vinyl chloride resin, are liable to be deteriorated with either heat or light. Heretofore, there have been employed a number butadiene stabilizers, for example, inorganic metal salts such as tribasic lead sulfate, metal soaps such as cadmium stearate, barium stearate, lead stearate, calcium stearate and zinc stearate, metal salts of substituted phenols such as barium nonylphenolate, organo tin compounds such as an alkyltin laurate, an alkyltin maleate and an alkyltin mercaptocarboxylic acid ester, epoxy compounds such as an epoxy resin and an epoxidated oil, phenol-like compounds and organic esters of phosphorus acid, for the purposes of preventing the aforementioned deteriorations occuring in processing these resins and in the use of the obtained product. Particularly, alkyltin mercaptocarboxylic acid esters are more excellent in either heat-stabilizing effect or in transparency so that glassy product can be obtained. These conventional esters, therefore, have been tested for the purpose of the application to the processing of such resins. However, these conventional esters emit unpleasant mercaptan odor in the manufacture which terribly lowers the working environment. Further, such unpleasant mercaptan odor remains on the obtained moulded product such as a film, sheet, bottle and the like, and which lowers the value of the products. In addition, conventional alkyltin mercaptocarboxylic acid esters can hardly bring about lubricant effect into the resins, and therefore a large amount of lubricants are compounded for the purpose of lubricating. Improvements in the odor and the lubricating effect have been, heretofore, contemplated by elevating boiling points of such alkyltin mercaptocarboxylic acid esters by way of increasing the molecular weight of an alkyltin mercaptocarboxylic acid esters.
In general, the molecular weight of an alkyltin mercaptocarboxylic acid ester may be increased by having the molecular weight of a mercaptocarboxylic acid ester portion increased. The molecular weight of the mercaptocarboxylic acid ester may be increased through employing either a higher molecular weight mercaptocarboxylic acid or a higher molecular weight alcohol. Generally, employment of a higher molecular weight alcohol may be effective in increasing the molecular weight of the mercaptocarboxylic acid ester.
It is well known that either ester formation by reaction of an acid with an alcohol or interesterification is conducted in the presence of an acid or base catalyst. Further, it is known that the employed catalyst is necessarily removed from the stabilizer because such a catalyst may be almost harmful to a resin in which the stabilizer is incorporated. Separation of the catalyst from the resulting ester may preferably be effected by distillation of the ester after washing with water, and, for this reason, the resulting ester preferably has a low boiling point. At least, the resulting ester must be distillable at a reduced pressure. Accordingly, the ester formation has, heretofore, been effected so as to yield a higher molecular weight mercaptocarboxylic acid ester in advance of formation of its tin compound, as disclosed in U.S. Pat. Nos. 2,641,596 2,648,650, 2,752,325 and 3,832,750.
However, a molecular weight increased mercaptocarboxylic acid ester has a rather higher boiling point, and the resulting ester is partly decomposed during the distillation at an elevated temperature. The decomposed esters generally impart malodor to the resin in which the stabilizer is incorporated.
The ester formed by the reaction may be employed as the stabilizer without purification, but crude one inevitably imparts malodor to the resin.